Uninterruptible power supply device with circuit for degradation judgment of storage battery

ABSTRACT

There is herein provided an uninterruptible power supply device with a degradation judgment circuit  4  of a storage battery  2  which can perform an exact judgment, continuing the power supply to a load apparatus  8  stably without giving the excessive burden to the storage battery  2 . The storage battery  2  is floatingly charged from a rectifier  1  connected with the power source  10 . The device has the control circuit  3  for controlling the output voltage of the rectifier  1  and the degradation judgment circuit  4 . The output voltage of the rectifier  1  is lowered to below a steady state by the control circuit  3 . As a result, the storage battery  2  discharges with the current Idc restricted rather than rated discharge current. And a part of power supply is supplied to the load  8 . The degradation judgment circuit  4  judges the degradation of the storage battery based on the discharge voltage Vdc.

BACKGROUND OF THE INVENTION

[0001] This invention relates to an uninterruptible power supply deviceof computers or communication apparatuses, connecting to a circuit fordegradation judgment for a storage battery built therein.

[0002] Supplying a current from an alternating power to variouscommunication apparatuses and so on, the uninterruptible power supplydevice is inserted between the alternating power and such acommunication apparatus in order to prevent the power from stopping byits unexpected failure or an interception of a breaker and damaging theapparatus or interrupting work.

[0003] There are two types of a normal converter power supply system anda normal supply system from a commercial power roughly dividing suchuninterruptible power supply devices. The former is equipped with arectification circuit, a storage battery and a converter. It normallycarries out floating charge to the storage battery with a direct currentobtained from the rectification circuit and supplying an alternatingcurrent converting from the direct current by the converter to the loadapparatus. In the latter, the alternating current is directly suppliedfrom an alternating power to the load apparatus. On the other hand, thestorage batter is carried out such floating charge with a direct currentof an alternating-direct current conversion from the power.

[0004] If any type of the uninterruptible power supply devices stop tobe supplied power at power failure etc., the storage battery willdischarge and a direct-alternating current conversion of the dischargecurrent will be carried out. And as long as the discharge of the storagebattery continues, power is supplied and the load apparatus continues todrive without an intermission. If the power failure and so on stops inthe meantime, it will return to the usual power supply state.

[0005] The storage battery degrades by over discharge of itself ordrives of itself for a long range time. If the storage battery of theuninterruptible power supply device has degraded, discharge will notcontinue for a long time and the power source will not return in time,or if the degradation is remarkable, the discharge voltage isinsufficient to drive the load apparatus.

[0006] Therefore, an uninterruptible power supply device attaches acircuit for judging the degradation of the storage battery. It is mostgenerally known such a circuit judges by comparing a curve of theinstant discharge current of the storage battery and a discharge curveof a normal storage battery i.e. reference curve thereof. It is alsoknown that an impedance of such a storage battery is measured to judgethe degradation. Japanese Patent Provisional Publication No. 2000-50525discloses a method for judging the degradation by observing dischargeprogress of the storage battery when reducing a supplying voltage to theload from the power converter to make the storage battery discharge.

[0007] However, these prior judgment methods take a long time to makethe storage battery discharge until the curve of the discharge currentis obtained enough. A reference curve according to a kind of a storagebattery or/and a discharging rate thereof is required and that a memoryfor the reference curve is required. A setup thus becomes complicated.Moreover, judging promotes the degradation of the storage battery sincean unusual burden is applied thereto. Actually, when the storage batteryhas degraded, the discharge may stop during the judgment, and anoriginal function may be unable to be achieved as an uninterruptiblepower source.

SUMMARY OF THE INVENTION

[0008] The present invention has been developed to solve the foregoingproblems. It is an object of the present invention to provide anuninterruptible power supply device for supplying power to a load andcharging floatingly to a storage battery with the degradation judgmentcircuit of the storage battery which can perform an exact judgment,achieving an original function as an uninterruptible power source ofcontinuing the power to stably supply to the load apparatus withoutgiving the excessive burden to the storage battery.

[0009] The present invention was developed for accomplishing theforegoing object. The uninterruptible power supply device of the presentinvention is used for supplying power to a load and charging floatinglyto a storage battery from a converter connecting to a alternatingcurrent power source. The device comprises a control circuit forcontrolling an output voltage of the converter to lower below a steadystate, the storage battery thus to discharge at a more limited currentthan the rated current thereof, and the converter to supply a part ofload current to the load; and a judgment circuit for judging thedegradation of the storage battery based on the discharge voltage of thelimited discharge current.

[0010] In another aspect of the uninterruptible power supply device ofthe present invention comprises; a control circuit for controlling anoutput voltage of the converter to lower below a steady state, thestorage battery thus to discharge at a more limited current than therated current thereof, and the converter to supply a part of loadcurrent to the load; and a judgment circuit judges the degradation ofthe storage battery based on a charging time of the storage battery fromwhen controlling, by the control circuit, the converter to return theoutput voltage to the steady state until completing full charge statethereof.

[0011] In the uninterruptible power supply device of the presentinvention, the converter is a rectifier and the load may include adirect-alternating current inverter in addition to a whole loadapparatus.

[0012] In the present uninterruptible power supply device, the converteris a rectifier and a direct-alternating current inverter may beconnected on midway between the storage battery and the load.

[0013] In the present uninterruptible power supply device, the convertercomprises a mutual transducer of direct and alternating current. whichconnects to the power source in parallel with the load, and whichconnects the storage battery thereto.

[0014] In the present uninterruptible power supply device, the convertercomprises a transducer of alternating and direct current which connectsto the power source in parallel with the load, and which connects thestorage battery and a direct-alternating current inverter.

[0015] In the present uninterruptible power supply device, the limiteddischarge current of the storage battery, by controlling the outputvoltage of the converter to lower below the steady state, is almostconstant what is equivalent to 10-50% of the maximum current of theload. It is more prefer the limited discharge current of the storagebattery is controlled at a constant current of around 30% of the maximumcurrent of the load.

[0016] In the present uninterruptible power supply device, the controlcircuit connects to a trigger signal source which comprises memorymemorized an operational schedule of the degradation judgment, and theconverter starts to lower the output voltage at the timing of thetrigger signal and the storage battery then starts to discharge.

[0017] In the present uninterruptible power supply device, the converterand the control circuit comprise a rectifier for obtaining a directcurrent from the alternating current power source, and a closing loopfor bringing the voltage of the direct current close to an appointeddirect current voltage with a pulse duration modulation control for analternating input voltage of itself.

[0018] In the present uninterruptible power supply device, thedegradation judgment circuit comprises a comparator for comparingbetween an appointed value of a direct current voltage from the controlcircuit and the discharge voltage of the storage battery.

[0019] In the present uninterruptible power supply device, thedegradation judgment circuit comprises an integration circuit forintegrating with a voltage difference between the appointed value of thedirect current voltage form the control circuit and a discharge voltageof the storage battery, and a comparator for comparing between theoutput voltage of the integration circuit and a standard voltage.

[0020] In the other aspect of the uninterruptible power supply device ofthe present invention, the degradation judgment circuit comprises atimer for measuring the charge time of the storage battery.

[0021] In the other aspect of the present uninterruptible power supplydevice, the degradation judgment circuit comprises a timer connecting toa comparator for comparing a charging current of the storage batterywith a base current.

BRIEF EXPLANATION OF DRAWINGS

[0022]FIG. 1 is a block circuit diagram showing an example ofcomposition of the uninterruptible power supply device with thedegradation judgment circuit of the storage battery which applies thepresent invention.

[0023]FIG. 2 is a block circuit diagram showing an example of thecontrol circuit of the uninterruptible power supply device with thedegradation judgment circuit of the storage battery which applies thepresent invention.

[0024]FIG. 3 is a waveform diagram explaining a circuit operation of theuninterruptible power supply device with the degradation judgmentcircuit of the storage battery which applies the present invention.

[0025]FIG. 4 is a block circuit diagram showing another example of thecomposition of the uninterruptible power supply device with thedegradation judgment circuit of the storage battery which applies thepresent invention.

[0026]FIG. 5 is also a block circuit diagram showing another example ofthe composition of the uninterruptible power supply device with thedegradation judgment circuit of the storage battery which applies thepresent invention.

[0027]FIG. 6 is a block circuit diagram showing an example ofdegradation judgment circuit of the storage battery of theuninterruptible power supply device with the degradation judgmentcircuit of the storage battery which applies the present invention.

[0028]FIG. 7 is similarly a block circuit diagram showing anotherexample of degradation judgment circuit of the storage battery.

[0029]FIG. 8 is similarly a block circuit diagram showing anotherexample of degradation judgment circuit of storage battery.

DETAILED DESCRIPTION OF THE INVENTION

[0030] Preferable examples of the present invention will be belowexplained in detail seeing drawings.

[0031]FIG. 1 shows a block circuit diagram of an example of theuninterruptible power supply device with the degradation judgmentcircuit of the storage battery, which applies the present invention, isso called as a normal inverter power supply system.

[0032] In the uninterruptible power supply device of FIG. 1, a rectifier1 is connected to a power source of commercial alternating current 10,and a storage battery 2 and a load apparatus 8 through an inverter 6 areconnected to the output side thereof. A control circuit 3 is connectedto the rectifier 1, refer FIGS. 1 and also 2, of which direct currentoutput is controlled in an optional constant voltage. A degradationjudgment circuit 4 for battery based on discharge voltage of the storagebattery is connected to the control circuit 3 with a trigger signal forstarting operation thereof.

[0033] The rectifier 1, in FIG. 2, to which the control circuit isconnected for obtaining output of a direct current voltage Vdc from thepower source of the commercial alternating current 10 aiming at anappointed value Vdc* of a direct current voltage. From the appointedvalue Vdc* of the direct current voltage, a voltage comparator 23, PIDcontrol device 24, that is a Proportional-Integral-Derivative control,and a pulse width modulation (PWM) 25 are connected in this order, andthen the direct current voltage Vdc is output. The direct currentvoltage Vdc feeds back to the voltage comparator 23 and thus constitutesa closing loop.

[0034] The uninterruptible power supply device of FIG. 1 convertsalternating current from the commercial power source to a constantvoltage direct current wit the rectifier 1 and the control circuit 3under the steady state. The input alternating current is controlled withthe pulse width modulation and repeatedly controlled with the closingloop to approach the appointed value Vdc* of the direct current voltagewhich is set up in the control circuit 3, and which is then output underthe steady state. The direct current output carries out the floatingcharge of the storage battery 2, changes to a sine wave voltage, that isan alternating current, with the inverter 6, and then the changedalternating current is supplied to the load apparatus 8.

[0035] When power stops from the power source of commercial alternatingcurrent 10 at a power failure and so on, the storage battery 2discharges and its discharge current is changed into alternating currentwith inverter 6. The load apparatus 8 continue to be supplied of powerand operate without an intermission as long as continuing of dischargefrom the storage battery 2. If the power failure and so on stops in themeantime, it will return to the usual power supply of the steady state.

[0036] In order to judge the degradation of the storage battery 2, theappointed value Vdc* of the direct current voltage of the controlcircuit 3 is lowered and then the output voltage of the rectifier 1 islowered to below the steady state at the time of inputting of thetrigger signal to the control circuit 3. In this example, thedegradation is judged by setting up the appointed value Vdc* of thedirect current voltage so that the storage battery 2 discharges thecurrent equivalent to 30% of the maximum current of the load apparatus8.

[0037] In the storage battery 2 of this example, 168 storage cells ofrated voltage 2V per one connects in series to each other so that therated voltage thereof is 336 V. The appointed value Vdc* of the directcurrent voltage set in the control circuit 3 under the steady state is382 V of floating charge voltage, namely 2.275 V per a cell. The outputvoltage of the rectifier 1 is controlled to 382V by the closing loopfunction of the control circuit 3 under the steady state. When thetrigger signal inputs in the control circuit 3, the appointed value Vdc*of the direct current voltage is set to 340V, namely 2.024 V per a cell,and the degradation is judged by operating the closing loop function ofthe control circuit 3. Consequently, 30% of discharge current Idc of thestorage battery 2 and 70% of current from the rectifier 1 inputs intothe inverter 6 if the load apparatus 8 is operating with the greatestcurrent. The control circuit 3 keeps the appointed value Vdc* of thedirect current voltage constant. If an actuating current of the loadapparatus 8 decreases from the maximum, the discharge current Idc of thestorage battery 2 will be kept constant and the current from therectifier 1 will decrease. Therefore, if the actuating current of theload apparatus 8 is 50% of the maximum, 30% of the discharge current Idcof the storage battery 2 and 20% of the current from the rectifier 1 areinput. That is to say, if the discharge current of the storage batteryis set to 30%, the examination can start when the rate of load is over30%.

[0038]FIG. 3 shows the waveform of the actuating current when judgingthe degradation of the present uninterruptible power supply device withthe degradation judgment circuit of the storage battery and when beforeand after the judgment. The input current Iin from the power source ofcommercial alternating current 10 controlled to the sign wave start tothe degradation judgment with a trigger signal, see (A), the amplitudedecreases maintaining the sine wave since, see (C), the dischargecurrent of the storage battery is added. As the current Idc from thestorage battery 2 is added to the output current of the rectifier 1, itis constant that the whole current flows into the inverter 6. Therefore,see (D), the output alternating current lout from inverter 6, that isthe current supplied to the load apparatus 8, is constant. Even if thedegradation judgment is carried out, the load apparatus 8 can continueoperation similar to the steady state.

[0039]FIG. 3(B) shows the rated voltage, an appointed value Vdc* of thedirect current voltage, and discharge voltages of the storage battery 2.As shown in (B), a potential difference ΔVdc1 between a dischargevoltage Vdc1 and the appointed voltage Vdc* is large if the storagebattery 2 is normal. A potential difference ΔVdc2 between a dischargevoltage Vdc2 and the appointed voltage Vdc* is small if the storagebattery 2 has degraded. In the degradation judgment circuit 4 for thestorage battery by the discharge, normal or degradation of the storagebattery 2 is distinguished strengths of the discharge voltages ΔVdc inthe state to be judged, refer FIGS. 6 and 7.

[0040] For example, when a appointed value Vdc* of the direct currentvoltage is lowered to 340V in degradation judgment state, a dischargevoltage of new storage battery 2 is 346V but a discharge voltage of astorage battery degraded in about 50% is 342V. The degradation can bejudged by such distinction of the strength of the discharge voltage.

[0041] After time T have passed, returning the set of the appointedvoltage Vdc* of the control circuit 3 to 382V of the steady state from340V of the degradation judgment state, the output voltage Vdc of therectifier 1 builds up gradually to 382V with the closing loop functionof the control circuit 3, restricting the charge current to the storagebattery. Therefore, as shown in FIG. 3(C), the storage battery 2discharged as current Idc until that moment turns to be charged from therectifier 1. That means that the current Idc of the storage battery 2changes the charge current indicated the negative side from thedischarge current indicated the positive side. The storage battery 2 isthen saturated with the charge by passing time t.

[0042]FIG. 4 is the block circuit diagram showing another example of acomposition of the present uninterruptible power supply device with thedegradation judgment circuit of the storage battery. The uninterruptiblepower supply device is a normal supply system from a commercial power.

[0043] As shown in FIG. 4, a load apparatus 8 is connected to the powersource of commercial alternating current 10 through a switching circuit9. A converter 12 as for converting mutually alternating-direct currentor direct-alternating current is also connected thereto in parallel withthe load apparatus 8. The control circuit 3 is connected to theconverter 12, and the storage battery 2 is also connected to theconverter 12. An ammeter 7 is connected to the output side of thestorage battery 2 and also to the degradation judgment circuit 5 for thestorage battery 2 by the charge time thereof. A trigger signal of thedegradation judgment 5 can input to the control circuit 3 and thedegradation judgment circuit 5. The control circuit 3 is the samecomposition as what is shown in FIG. 2.

[0044] In the uninterruptible power supply device, the switching circuit9 turns on under the steady state and, thus, power is directly suppliedto the load apparatus 8 from the power source of commercial alternatingcurrent 10. On the other hand, the converter 12 convertsalternating-direct current to floating the storage battery 2. If thepower from the power source of commercial alternating current 10 stopsby the power failure and so on, the switching circuit 9 operates toswitch off. Then the storage battery 2 discharges and the converter 12converts direct-alternating current from its discharge current. The loadapparatus 8 continue to be supplied of power and operate without anintermission as long as continuing of discharge from the storage battery2. If the power failure and so on stops in the meantime, the switchingcircuit 9 switches on and it return to the usual power supply from thepower source of commercial alternating current.

[0045] The degradation judgment operation and the time chart of thecontrol circuit 3 of the uninterruptible power supply device shown inFIG. 4 is the same as that of FIG. 1 so that such explanation is omittedfor avoiding duplicate description. However, the circuit operationdiffers a little at a point of the degradation judgment circuit 5 baseson the charge time of the storage battery.

[0046] As shown in FIG. 3(C), after ending the discharge with therestricted current restricted for the degradation judgment of thestorage battery, that means the time T passes, if the storage battery 2is normal, the charge continues for a long time as seen t2, but if thestorage battery 2 is degraded, the charge completes for a short time asseen t1. Therefore, the normality or the degradation of the storagebattery is distinguished by measuring the time t with a timer in thedegradation judgment circuit 5.

[0047] For example, when an appointed value Vdc* of a direct currentvoltage is lowered to 340V and a discharge time T takes 15 seconds, acharge time t of a new storage battery 2 is 12 seconds, but a chargetime t of a storage battery 2 degraded about 50% of its capacity is 4seconds. The degradation is thus judged by measuring the charge time t.

[0048]FIG. 5 is also a block circuit diagram showing another example ofthe composition of the uninterruptible power supply device with thedegradation judgment circuit of the storage battery which applies thepresent invention. This type of the uninterruptible power supply deviceis a normal supply system from a commercial power and, however, isdifferent in aspect of the device from the above one.

[0049] As shown in FIG. 5, the load apparatus 8 through the switchingcircuit 9 is connected to the power source of commercial alternatingcurrent 10. The rectifier 1 as the transducer and the inverter 6 arealso connected thereto. The output side of the inverter 6 is connectedto the load apparatus 8. The control circuit 3 is connected to therectifier 1. The degradation judgment circuit 4 of the storage batterybased on the discharge voltage of the storage battery is connected tothe control circuit 3. The storage battery 2 is connected between therectifier 1 and the inverter 6. Moreover, the schedule timer 14 whichgenerates the trigger signal for the degradation judgment of the storagebattery is also connected to the control circuit 3. The control circuit3 is the same composition as what is shown in FIG. 2.

[0050] In the present uninterruptible power supply device, the switchingcircuit 9 is turned on under the steady state, so the power is directlysupplied to the load apparatus 8 from the power source of commercialalternating current 10. On the other hand, the floating charge iscarried out to the storage battery 2 by the direct current from therectifier 1. The switching circuit 9 operates if the power from thepower source of commercial alternating current 10 stops by the powerfailure and so on. Then the storage battery 2 discharge anddirect-alternating current conversion of its discharge current arecarried out at the inverter 6. The converted alternating current issupplied to the load apparatus 8. If the power failure and so on stopsin the meantime, the switching circuit 9 switches on to return to theusual power supply from the power source of commercial alternatingcurrent.

[0051] The explanation of operation containing the circuit of thecontrol circuit 3 and the time chart in the degradation judgmentoperation of the uninterruptible power supply device with thedegradation judgment circuit of the storage battery shown in FIG. 5 isthe same as that of FIG. 1. But the degradation judgment of the storagebattery is periodically started based on the trigger signal which isgenerated by the schedule timer 14 according to the maintenance cycle ofthe apparatus.

[0052]FIG. 6 is the circuit diagram showing a concrete example ofcomposition of the degradation judgment circuit 4 of the storage batteryshown in FIG. 1 and FIG. 5. This type of a degradation judgment circuit4 of the storage battery is based on discharge voltage of the storagebattery 2, and has a direct current power source 16 and a voltagecomparator 18. As shown in FIG. 3(B), a voltage ΔVdc, that is apotential difference between the discharge voltage Vdc of the storagebattery 2 and the appointed value Vdc* of the direct current voltage atthe time of the degradation judgment of the storage battery, is large ifthe storage battery 2 is normal, but is small if the storage battery 2has degraded. The voltage ΔVdc and a voltage of the power source 16 iscompared by the voltage comparator 18. Then a normal signal is obtainedfrom the voltage comparator 18 if the former one is larger, or else adegradation signal is obtained.

[0053]FIG. 7 is also the circuit diagram showing another example ofcomposition of the degradation judgment circuit 4 of the storage batterybased on the discharge voltage of the storage battery shown in FIG. 1and FIG. 5. This type of a degradation judgment circuit 4 of the storagebattery, the degradation is also judged based on the potentialdifference ΔVdc. The value of the voltage ΔVdc of the potentialdifference is so small that it is difficult to handle. Therefore, thevoltage ΔVdc of the potential difference is integrated with time T atthe integrator 15 and then the integrated value of the voltage ΔVdc andthe voltage of the power source of base voltage 17 is compared by thevoltage comparator 19.

[0054] The degradation judgement circuit based on the discharge voltageof the storage battery 2 shown in FIG. 6 and FIG. 7 can be applied tothe uninterruptible power supply device shown in FIG. 4 as well as theone shown in FIG. 1 and FIG. 5.

[0055] The degradation judgment circuit 5 of the storage battery shownin FIG. 4 is on the charge time and is fundamentally composed of thetimer. A concrete example of the degradation judgment circuit 5 of thistype can also be used as shown in FIG. 8. The circuit 5 has a powersource 20 of a base current, a current value comparator 21 and a timer22. The charge current Idc of the storage battery 2 and a current fromthe power source 20 is compared by the current value comparator 21 andtime is measured by the timer 22 while the charge current Idc is largerthan the current of the power source 20. The normal signal is given ifthe measured time is long, or else a degradation signal is given.

[0056] The degradation judgment circuit based on charge time can beapplied to the uninterruptible power supply device shown in FIG. 1 andFIG. 5 as well as that shown in FIG. 4.

[0057] Furthermore, both degradation judgment circuits 4 of the storagebattery based on the discharge voltage and on charge time can also beapplied to the uninterruptible power supply device which supplies thedirect current. In the uninterruptible power supply device, the inverter6 and the load apparatus 8 are collectively considered as the load 11 inthe circuit shown in FIG. 1.

[0058] The schedule timer 14, which generates the trigger signal for thedegradation judgment of the storage battery shown in FIG. 5, is appliedto the uninterruptible power supply device shown in FIG. 1 and FIG. 4.

[0059] As a whole, illustrated or described circuits or elements can becarried out in all combination within a range of the essence of thepresent invention.

[0060] As it is mentioned above in detail, the judgment of the storagebattery by the present uninterruptible power supply device with thedegradation judgment circuit of the storage battery can judge exactly inshort time without the unnecessary burden to the storage battery sincethe storage battery is not made to discharge with a long time or largecurrent. The uninterruptible power supply device does not lead toso-called destructive inspection. The present uninterruptible powersupply device can judge exactly and supplies stably source to load sothat is very preferable to automatically and intentionally maintain astorage battery without stopping the load apparatus.

1. An uninterruptible power supply device for supplying power to a loadand charging floatingly to a storage battery from a converter connectingto a alternating current power source, with the degradation judgmentcircuit of the storage battery, comprising; a control circuit forcontrolling an output voltage of the converter to lower below a steadystate, the storage battery thus to discharge at a more limited currentthan the rated current thereof, and the converter to supply a part ofload current to the load; and a judgment circuit for judging thedegradation of the storage battery based on the discharge voltage of thelimited discharge current.
 2. An uninterruptible power supply device forsupplying power to a load and charging floatingly to a storage batteryfrom a converter connecting to a alternating current power source, withthe degradation judgment circuit of the storage battery, comprising; acontrol circuit for controlling an output voltage of the converter tolower below a steady state, the storage battery thus to discharge at amore limited current than the rated current thereof, and the converterto supply a part of load current to the load; and a judgment circuitjudges the degradation of the storage battery based on a charging timeof the storage battery from when controlling, by the control circuit,the converter to return the output voltage to the steady state untilcompleting full charge state thereof.
 3. The uninterruptible powersupply device according to claim 1, wherein said converter is arectifier and said load includes a direct-alternating current inverterin addition to a whole load apparatus.
 4. The uninterruptible powersupply device according to claim 1, wherein said converter is arectifier and a direct-alternating current inverter is connected onmidway between the storage battery and the load.
 5. The uninterruptiblepower supply device according to claim 1, wherein said convertercomprises a mutual transducer of direct and alternating current, whichconnects to the power source in parallel with the load, and whichconnects the storage battery thereto.
 6. The uninterruptible powersupply device according to claim 1, wherein said converter comprises atransducer of alternating and direct current which connects to the powersource in parallel with the load, and which connects the storage batteryand a direct-alternating current inverter.
 7. The uninterruptible powersupply device according to claim 1, wherein said limited dischargecurrent of the storage battery, by controlling the output voltage of theconverter to lower below the steady state, is almost constant what isequivalent to 10-50% of the maximum current of the load.
 8. Theuninterruptible power supply device according to claim 1, wherein saidcontrol circuit connects to a trigger signal source which comprisesmemory memorized an operational schedule of the degradation judgment,and the converter starts to lower the output voltage at the timing ofthe trigger signal and the storage battery then starts to discharge. 9.The uninterruptible power supply device according to claim 1, whereinsaid converter and said control circuit comprise a rectifier forobtaining a direct current from the alternating current power source,and a closing loop for bringing the voltage of the direct current closeto an appointed direct current voltage with a pulse duration modulationcontrol for an alternating input voltage of itself.
 10. Theuninterruptible power supply device according to claim 1, wherein saiddegradation judgment circuit comprises a comparator for comparingbetween an appointed value of a direct current voltage from the controlcircuit and the discharge voltage of the storage battery.
 11. Theuninterruptible power supply device according to claim 1, wherein saiddegradation judgment circuit comprises an integration circuit forintegrating with a voltage difference between the appointed value of thedirect current voltage form the control circuit and a discharge voltageof the storage battery, and a comparator for comparing between theoutput voltage of the integration circuit and a standard voltage. 12.The uninterruptible power supply device according to claim 2, whereinsaid degradation judgment circuit comprises a timer for measuring thecharge time of the storage battery.
 13. The uninterruptible power supplydevice according to claim 2, wherein said degradation judgment circuitcomprises a timer connecting to a comparator for comparing a chargingcurrent of the storage battery with a of base current.
 14. Theuninterruptible power supply device according to claim 2, wherein saidconverter is a rectifier and said load includes a direct-alternatingcurrent inverter in addition to a whole load apparatus.
 15. Theuninterruptible power supply device according to claim 2, wherein saidconverter is a rectifier and a direct-alternating current inverter isconnected on midway between the storage battery and the load.
 16. Theuninterruptible power supply device according to claim 2, wherein saidconverter comprises a mutual transducer of direct and alternatingcurrent, which connects to the power source in parallel with the load,and which connects the storage battery thereto.
 17. The uninterruptiblepower supply device according to claim 2, wherein said convertercomprises a transducer of alternating and direct current which connectsto the power source in parallel with the load, and which connects thestorage battery and a direct-alternating current inverter.
 18. Theuninterruptible power supply device according to claim 2, wherein saidlimited discharge current of the storage battery, by controlling theoutput voltage of the converter to lower below the steady state, isalmost constant what is equivalent to 10-50% of the maximum current ofthe load.
 19. The uninterruptible power supply device according to claim2, wherein said control circuit connects to a trigger signal sourcewhich comprises memory memorized an operational schedule of thedegradation judgment, and the converter starts to lower the outputvoltage at the timing of the trigger signal and the storage battery thenstarts to discharge.
 20. The uninterruptible power supply deviceaccording to claim 2, wherein said converter and said control circuitcomprise a rectifier for obtaining a direct current from the alternatingcurrent power source, and a closing loop for bringing the voltage of thedirect current close to an appointed direct current voltage with a pulseduration modulation control for an alternating input voltage of itself.